Tar-bonded magnesia brick and method



pressing and to do no more.

nite States This invention relates to a liquid tar-bondable refractory mix composed of dolomite or dolomite and magnesite, and to a brick pressed from the same material. The invention also relates to a method of making the brick.

The liner engaged by the molten metal in an L-D (Leitz-Donowitz) iron-to-steel converter is made of tarbonded magnesia-containing bricks which at present are composed of both dolomite and magnesite in varying percentages. Generally, in back of the brick lining, a ram mix of approximately the same composition is used.

The principal object ofthis invention is to make a tarbonded brick and mix by a cold process, but as will appear, in attaining this object applicants have been able to make a hydration-resistant brick of 100% dead-burned dolomite. At the present time, a tar-bonded magnesia brick is made from both dolomite and magnesite by a hot process. A substantial proportion of the more expensive magnesite is used as fines because of its hydrationresistant and refractory properties. The present process consists of separately heating to 200 F. and above, rather coarse granulated dead-burned dolomite, dead-burned magnesite fines, and a pitch having a melting point of about 150 to 320 F. They are then thoroughly mixed in a heated mixer, and theresulting mix is pressed into bricks. After removal from the press, the bricks are cooled and they are ready for shipment. Where a ramming compound is desired, the pressing step is omitted and the mix bagged.

The process is diiiicult to practice commercially because pitch is a complicated mixture of carbon-bearing molecules, some of which are highly volatile. The pressability of the mixture is dependent upon the viscosity of the pitch. If the heat of the mix at the time it is fed into the mold box is too low, with the pitch solidifying at about 280 F., the mix lacks plasticity and aproper brick is not produced. On the other hand if the heat is too high, or if the heat is correct but the mix is held too long in the heated mixer, volatiles escape and the brick will not press. In either case, the quality of the brick is inferior. v

From the foregoing, it is evident that the hot process is one which requires extreme care at each step under circumstances where it is not easy to maintain the critical temperatures and times. Moreover, dealing with hot materials is always more difiicult than dealing with materials at room temperature. A feature of applicants invention is the use of a tar which is liquid at the room temperatures of a plant in which the mixing is done. These temperatures in the coldest winter are rarely below 50 F., or in the summer about 90 F.

Another object of this invention is to add something to the mix which will make it possible to use liquid tar. When applicants first made their mix with liquid tar, they recognized that after the pressing, something more must be done. The heating of the mix in the hot process results in complicated chemical reactions which make it possible to cool the brick to room temperatures after the The brick resist hydration for suflicient time to lay the brick in the wall of a converter. Brick pressed from a cold mix of dolomite and magnesite granules and liquid tar-pitch is useless. In the cold process, applicants contemplated drying at 500 F. for many hours, but when this was done, while the atent Dolomite (CaO- MgO dead- 3,044,889 .Patented July 17, 1962 brick could be hacked and placed in the oven, during the heating, they swelled and cracked so as to be unusable. A feature of this invention is the addition of P 0 phosphorus pentoxide, to the mix and then after pressing, holding the brick at a temperature of 400 F. or more for sufiicient time to solidify the tar. The action of the P 0 and the general chemistry of the material is not understood. It is not believed that the P 0 in the cold mix before pressing has, much effect upon either the tar or the magnesite or the dolomite. As tests hereinafter set forth demonstnate, however, the P 0 upon heating the mix, has a definite effect in raising the resistance of the brick to the absorption of water vapor and seems to have some eifect upon vthetan.

A great advantage of applicants.use of P 0 primarily in the cold process, is that applicants can make a stable hydration-resistant brick from dead-burned dolomite, CaO-MgO. Refractory manufacturers have sought to make such a brick because dead-burned dolomite is much lessexpensive than dead-burned magnesite, and the fusion point of dead-burned dolomite is not sufficiently lower than that of dead-burned magnesite to limit the use of a dolomite brick in furnaces. However, the dolomite picks up water vapor so rapidly that storing even for a few days results in disintegration and sp alling. Users, have insisted that the time lapse between pressing the brick and installation in a furnace be as short as possible. Some brick makers wrap tar-bonded dolomite and magnesite brick in water vapor-impervious paper; The

phosphorus pentoxide in some manner retards hydration 7 As tests show, applicants dolomite of the calcium oxide. bricks show little hydration as evidenced by cracking even after long exposureto ordinary atmospheric humidity.

Applicants cold mix of dolomite alone, or dolomite and magnesite, pitch and phosphoruspen-toxide may be used as a ramming mixbetween the converter Wall and fact that applicants can use either oil-coated or uncoated dolomite granules. In making a tar-bonded brick containing dolomite, uncoated granules are often used. In applicants process, either coated or uncoated dolomite granules may be used. .7 7

Still another object of this invention is to improve the water-resistant properties of brick made by the hot process. As tests set forthtbelow indicate, the addition of P 0 to either COIdJOI hot mixes results in a brick which picks up substantially less water after ten days of standing in a room at atmospheric humidity than does the same brick without the P 0 I Y MIXES FOR COLD PROCESS The-following four mixes have been selected for the purpose of showing'that the percentage of..'P O in the mix does-notse'em to be aifected ,by different relative amounts of the magnesite and the dolomite used: I i

. 7 Mix 1 Pericla'se MgO dea d burned magnesite) p 42%.

burned) 58%. Liquid tar 5.5% of the combined weight of periclase and dolomite. P 0 2% of the combined weight of periclase and dolomite.

3 Mix 2 Periclase (MgO-dead-burned magnesite) 40%. Dolomite (CaO-MgO deadburned) 60%.

Liquid tar 5.5% of the combined weight of periclase and dolomite.

P 2% of the combined weight of periclase and dolomite.

Mix 3 Periclase (MgO-dead-burned magnesite) 35%. Dolomite (CaO-MgO deadburned) 65%. Liquid tar 5.5% of the combined weight of periclase and dolomite.

P 0 2% of the combined weight of periclase and dolomite.

Mix 4 Dolomite 100%.

Liquid tar 5.5% of the weight of the dolomite.

P 0 2% of the weight of the dolomite.

The word periclase is used instead of magnesite to identify a dead-burned magnesite having a very high percentage of MgO. It is a common term used in the trade and is an item which has been processed as by dead-burning. Dolomite means dead-burned dolomite. As will be appreciated, the mixture will work whether the dead-burned dolomite is oil-treated or not.

The liquid tar is a mixture of hydrocarbons and their derivatives. It includes substantial percentages of volatiles which vaporize with heat and agitation. The particular product used by applicants is Koppers No. 92258, and it is identified as the first product in the distillation of the residue from coking ovens which is obtained after the removal of naphthalene. This viscosity of this product can be raised by adding solid pitch which dissolves in it, and the viscosity can be lowered by adding more volatile fractions such as mineral spirits and other commonly used solvents. The desired viscosity is determined by whether or not it will hold the components of the brick together after pressing so that the edges and the corners are well defined. In practice, the tar compound used has been dehydrated and in all of the experiments of the applicants and in the mixtures described herein, a dehydrated liquid tar has been used.

The P 0 is in powder form.

A screen analysis of the dolomite and periclase is as follows:

Percent Dead-burned dolomite through a 3-mesh 6 Dead-burned dolomite through a 4-mesh 16.4 Dead-burned dolomite through a 6-mesh 13.7 Dead-burned dolomite through a l0-mesh 16.8 Dead-burned dolomite through a ZO-mesh 4.2 Dead-burned periclase through a -mesh 40 The percentages are approximate, and it will be observed that all of the powdered material is magnesite. The analysis is that for Mix 2 above. The foregoing is a somewhat standard screen analysis. The percentages are obtained by applicants blending two or more screened fractions. Screen sizing is important for a proper mix, but the above screen analysis and variations thereof are well known. The relative sizes will be adhered to in Mix 4, the 20 ore fines being of dead-burned dolomite. Granulated dolomite and periclase are obtained in the trade til as a standard product. The screen analysis above was made from this product.

The process of mixing is this: The dead-burned dolomite (including all screen sizes for Mix 4) is poured into the mixer and then while the mixer is actuated, the liquid tar is added. The P 0 is immediately added, followed by the periclase for Mixes l, 2 and 3. The mixing requires about five minutes. If the mix is to be used for ramming, it is placed in bags which are sealed. If the mix is to be pressed into brick, it is immediately fed into the mold boxes and the brick pressed. Thereafter, the brick is dried for 36 hours at a temperature of 550 P.

All of the brick were evaluated from the standpoint of ability to resist water while standing on their ends at room temperature with room humidity. The evaluation of the tests must take into consideration variations in room humidity, particularly variations between the humidity in summer and that in winter; however, the tests were mostly conducted at humidities of around 25-30, and they were always comparable. In these tests, evaluation was also based upon cracking or spalling of the edges and corners or bloating, upon the modulus of rupture, the observable strength in passing through the temperature range of 300-1400 F., and density.

RATIO OF PERICLASE TO DOLOMITE One can make a usable brick with various proportions of periclase and dolomite in the first three mixes. With a given proportion of dolomite and periclase, different quantities of P 0 were used, commencing with of 1% to 5%. There was no perceptible ditference in the bricks.

THE AMOUNT OF P 0 REQUIRED Where of 1% of P 0 on the basis of the weight of the ore was used in mixes with the ore ranges of Mixes l to 3, no perceptible effect was observed. When a mix such as Mix 1 is pressed and no P 0 is added, the resulting brick will crack during the drying step. With of 1% of P 0 there is no observable difference. The brick disintegrate. When /2 of 1% was added, the results were mixed, that is to say, they were not predictable. 'In some heats, a brick would be obtained which did not crack during the heating. Fairly predictable results were attained with 1% or" P 0 A large number of heats were made with 2% of P 0 in mixes having different ratios of dolomite and magnesite. Applicants did not sustain a failure. A brick with 5% of P 0 was made, but its modulus of rupture and its ability to resist water did not seem superior to a brick with 2% of P 0 It is, of course, desirable to keep the P 0 at a minimum not only because of expense, but because phosphorus is not wanted in the liner to be released into the steel. Applicants seek just enough P 0 to prevent cracking during drying. Applicants most recent testing indicates that the range should be from l-2%, and that while 2% seems to be completely protective, l /2% is enough. Applicants have not had a failure on Mixes 1-3 where l /z% of the weight of the ores was P 0 PERCENTAGES OF LIQUID TAR Where the liquid tar is too thin, a good green bond is not attained because the tar does not perform the holding function. On the other hand, if it is too thick, it offers too great resistance to the pressing, and again a satisfactory green bond it not attained. Dehydrated liquid tar in a range of 46% is satisfactory. If the viscosity is right and there is an excess of tar, its sole detriment resides in the volume of the brick that it occupies. An excess of tar will decrease the density of the brick. Applicants usually use liquid tar in the amount of 5.5 of the combined weight of the ores.

P 0 IN HOT PROCESS The following two mixes were made in accordance with the hot process, that is, the ingredients were preheated,

then mixed in a heated vessel, and then pressed, although the mold box was not heated.

weight of the ores. 5% of the combined weight of the ores.

Pitch (280 F. melting point)- Mix 6 Periclase (MgO-dead-burned magnesite) 40%. Dolomite (CaO-MgOdeadburned) 60%.

Pitch (280 F. melting point) 5% of the combined weight of the ores.

Both mixes'were pressed into brick on the same day. The bricks were then placed on a shelf in the laboratory exposed to room temperature and humidity. Twenty-one days later, the brick from Mix 6 was a semi-pile of granulated material. It could scarcely be identified as having once been a brick. The brick from Mix 5 on the same day showed only slight surface hydration. Applicants concluded that the P did one or both of two things. During the period when it was at approximately 300 F. in the mixing and pressing, it combined with one of the other ingredients to make a surface more impervious to the penetration of water; or because of its ability to readily combine with water, as the brick during storage picked up water, the P 0 combined with it. Applicants concluded that the P 0 performs its function in either the hot process or the cold process.

However, another test indicates that the P 0 performs its function much better in the cold process than in the hot process. The following mixes were made on the same day:

Mix 7 Periclase (MgOdead-burned magnesite) 40%. Dolomite (CaO MgO-deadburned) 60%. P 0 /2% weight of the ores.

Liquid tar-pitch 5% Weight of the ores.

After pressing the brick were held at 550 F. for 36 hours.

Mix 8 Periclase (MgO-dead-burned magnesite) 40%. Dolomite (CaO MgO-deadburned) 60%. P 0 .5% weight of the ores. Liquid tar-pitch 5.5% weight of the ores.

All ingredients preheated and mixed at about 400 F., and

after pressing cooled. The hot pressed rick of M X produced a brick which was badly hydrated nineteen days after the pressing. The cold pressed brick showed no signs of hydration 107 days after the pressing, although both bricks were placed on the same shelf at the same time.

EQUIVALENTS FOR P 0 Applicants have made some experiments with other compounds. Phosphoric acid and sulphuric acid were tried and dismissed because a good brick was not obtained. Calcium chloride was found to be of no value, possibly because it had no action on the tar or could not combine with water effectively in the presence of the tar. The calcium chloride did not interfere with the green strength of the brick so that it was possible to dry it for 36 hours at 550 F., but after one day of standing, the

brick had picked up a substantial amount of water. Carbamide phosphoric indicates thatit will work, that is, it will not interfere with the green strength and will increase water resistance, but this product is commercially not competitive.

THE PROCESS OF MAKING THE BRICK The process of making the brick is pressing and drying and the only critical step is the holding temperature and its duration. It is believed that the action of the P 0 provides the superior strength when the brick thereafter is carried through 1400 F. in the drying ovens and is completed at some point in excess of 25 hours. A holding temperature in excess of 700 F. is notbelieved to be necessary. In practice, applicants bring the brick up to 550 F. in the drying oven and hold it there for 36 hours. By raising the temperature and decreasing the time, comparable results can be obtained, but in one experiment 'at 550 F. for 20 hours, the brick was not as satisfactory from the point of View of water resistance.

APPEARANCE OF END PRODUCT The preferred brick after drying is substantially black. Its edge and corners are as well shaped and firm, although rougher than the edges and corners of an ordinary wood desk. Its modulus of rupture is 1600 psi. A four-inch brick ,cannot be broken in the hands of an ordinary man, and it is difficult with the finger to detach at an edge or corner any of the material. In contrast, a brick made by the cold process from the same batch, but

without the P 05, will be 5% larger, it can be broken in a the hand or chipped with the finger nails, its interior appears to be punky. These comparisons are of two bricks shortly after they left the drying oven. On exposure to room temperature and humidity for a few days, the brick without the P 0 will disintegrate.

Having thus described our invention, what we claim is:

1. A refractory mixture consisting essentially of granules composed principally of magnesia-bearing minerals of the group consisting of dolomite, magnesite and periclase in an amount in excess of of the total weight of the mixture, and the balance being phosphorus pentoxide in excess of 1%, and a bonding substance from the group consisting of tars and pitches consisting essentially of hydrocarbons in excess of 4%, both percentages being of the total weight of the magnesia-bearing minerals.

2. A refractory brick consisting essentially of granulated magnesia-bearing minerals of the group consisting of dolomite, magnesite and periclase, bonded by 4-6% of the group consisting of tar and pitch and .5 to 5% P 0 both percentages being of the weight of the minerals.

3. The method of making a bonded refractory mix which comprises mixing P 0 into a mixture of magnesiabearing minerals of the group consisting of dolomite, magnesite and periclase, and a bonding substance from the group consisting of tars and pitches consisting essentially of hydrocarbons, the amount of P 0 being between .5 to 5% by weight of the magnesia-bearing minerals,

and the amount of bonding substance being between 1 and 6% by weight of the said minerals.

4. The method of making a bonded basic brick which comprises the steps of forming a mixture consisting essentially of magnesia-bearing minerals of the group consisting of magnesite, dolomite and periclase in an amout in excess of 85% of the mixture, a bonding substance from the group consisting of tars and pitches consisting essentially of hydrocarbons, and P 0 the amount of bonding substance being from 46% and the amount of the P 0 being from .5 to 5%, both by weight of the minerals, and pressing said mix into bricks.

5. The method of claim 4 wherein said mixing steps are performed at temperatures of 60l00 F., and of thereafter holding said bricks at a temperature of 400- 600 F. for more than 25 hours, and-then cooling to room temperature.

6. The refractory mixture of claim 1 wherein the mineral granules consist substantially of dead-burned dolomite alone.

7. The refractory mixture of claim 1 wherein the granules of magnesia-bearing minerals of the group consisting of magnesite, dolomite and periclase are in mesh sizes of +20 to 20.

8. A refractory mixture consisting essentially of granulated dead-burned dolomite and periclase of varying sizes from +3 mesh to 20 mesh, tar liquid at room temperatures in an amount of 46% by weight of the dolomite and periclase, and P in an amount of l-2% by weight of the dolomite and periclase.

9. The refractory mixture of claim 8 wherein the percentage of liquid tar is approximately 5% and that of P 0 is approximately l /z%.

10. A refractory brick consisting essentially of granulated dolomite bonded by 46% of the group consisting of tar and pitch and .5 to 5% P 0 both percentages of the weight of the dolomite.

11. The refractory mixture of .claim 10 wherein the percentage of liquid tar is approximately 5% and that of P 0 is approximately 1 /2%.

12, A refractory brick consisting essentially of granulated magnesia, bonded by-46% tar and 1-2% P 0 of the Weight of the magnesia.

13. A refractory brick consisting essentially of magnesite, 6040% dolomite, 46% tar and l2% P 0 of the weight of the magnesite and dolomite.

14. A refractory brick consisting essentially of deadburned dolomite, 46% tar and l-5% P 0 said percentages being of the weight of the dolomite.

15. The method of claim 5 wherein the holding period is in the range of 30-40 hours.

16. The method of claim 5 wherein the temperature of the holding period is in the range of 525575 F.

Edson July 29, 1958 Martinet June 28, 1960 

2. A REFRACTORY BRICK CONSISTING ESSENTIALLY OF GRANULATED MAGNESIA-BEARING MINERALS OF THE GROUP CONSISTING OF DOLOMITE, MAGNESITE AND PERICLASE, BONDED BY 4-6% OF THE GROUP CONSISTING OF TAR AND PITCH AND .5% TO 5% P2O5, BOTH PERCENTAGES BEING OF THE WEIGHT OF THE MINERALS. 